Transport offload engines (TOE) include technology that is gaining popularity in high-speed systems for the purpose of optimizing throughput, and lowering processor utilization. TOE components are often incorporated into one of various printed circuit boards, such as a network interface card (NIC), a host bus adapter (HBA), a motherboard; or in any other desired offloading context.
In recent years, the communication speed in systems has increased faster than processor speed. This has produced an input/output (I/O) bottleneck. The processor, which is designed primarily for computing and not for I/O, cannot typically keep up with the data flowing through the network. As a result, the data flow is processed at a rate slower than the speed of the network. TOE technology solves this problem by removing the burden (i.e. offloading) from the processor and/or I/O subsystem.
Exemplary operation 100 of a TOE is set forth in prior art FIG. 1. As shown in the prior art diagram of FIG. 1, a local processor (of any sort) first sends to a TOE a command to transmit data, in order to transmit data corresponding to a transmission control protocol (TCP) connection from the processor having the attached TOE to a remote processor over a network. See operation 102.
Next, in operation 104, the TOE acquires the data, divides it into segments, and adds Ethernet, TCP, and Internet Protocol (IP) headers to each data segment to create a TCP/IP packet corresponding to each segment. Thereafter, the TOE transmits the resulting packets onto the network, as indicated in operation 106.
After the remote processor has received and validated the packets, the remote processor sends acknowledgements (ACKs) back to the local processor indicating how much of the data has been successfully received. Upon receiving an ACK for all the transmitted data (see decision 108), the TOE sends a command complete to the local processor indicating that the transmit command has been completed by the transport function of the TOE. See operation 110. Additional data may then be transmitted, as indicated in operation 112.
For the case in which an ACK is not received by the TOE within a predetermined time after the corresponding packets were sent, indicating an error condition, the TCP data is re-fetched from the TOE's memory. Note operation 114. In operation 116, the TOE can then retransmit some or all of the unacknowledged packets.
Thus, when transmitting data across a packet-switched network, data may be lost and such data must be retransmitted. For this reason, the TOE stores all unacknowledged data. However, with a 10 Gbps link and a possible 200 ms round-trip delay on a wide area network, this could mean that up to 10 Gbps*200 ms, or 2 gigabits, of information must be stored. Unfortunately, this is too much data to be stored in a cost effective manner on an integrated TOE, since integrating on-board memory on the TOE can be costly.
There is thus a need for a cost effective technique for performing network retransmission.